They are not used in Spot, and their interface is really horrible.  They
are used in SOG-ITS to implement the SLAP product from TACAS'11, so we
should support the functionality eventually, but maybe using the new
kind of properties that can be attached to automata.  In the meantime,
these classes are making refactoring harder.

* src/tgba/futurecondcol.cc, src/tgba/futurecondcol.hh,
src/tgba/tgbascc.cc, src/tgba/tgbascc.hh: Delete.
* src/tgba/Makefile.am, src/tgbatest/ltl2tgba.cc,
src/tgbatest/checkpsl.cc, src/tgbatest/emptchk.cc: Adjust.